Re: 1990 70hp evinrude randomly dies
did your symptoms start immediately following the carb rebuild 2 months ago, or before the rebuild, or some time after?
replacing spark plugs isn't the same as checking for spark.
To quickly determine whether spark is being produced is to pull a plug, reattach it to the boot, hold it against the block and look for spark during cranking. (use a plastic or insulated tool)
To test the quality of the spark, get an inline spark tester (couple bucks at autozone), set the gap for 7/16", clip it to the engine block, attach the plug leads (one at a time) and look for a strong blue spark while cranking. If it can't jump a half-inch gap in the open air without a spark plug, it's not firing in the hole under heat & compression.
When it dies, or when it won't start, are the plugs wet or dry after cranking? Do they all have the same appearance or is one different from the others?
While the engine's running, the bulb is just a fat spot in the fuel line -- fuel is flowing through it so it doesn't stay hard. But if the pump is keeping the carb bowls full, it will be firm when the engine shuts down, and should stay firm all day.
patrick is right, 70 PSI is too low, although equal across all cyl is good -- did you test a cold or warm engine? spin the engine several times on each hole?